A battery-powered hip exoskeleton weighing just 2.6kg has achieved what ankle-based wearable devices have repeatedly failed to do – meaningfully reduce the metabolic burden of walking in stroke survivors with hemiparesis. Researchers at the University of Utah report an 18% reduction in the energy cost of walking in seven patients. Their findings were published in February 2026 in Nature Communications.
© Dan Hixson, University of Utah
Stroke is the leading cause of long-term disability in the United States, with hemiparesis – weakness and impaired motor control on one side of the body – affecting around 80% of survivors. The consequence for walking is profound: individuals with hemiparesis expend roughly 60% more energy per stride than healthy walkers, leading to slower speeds, reduced endurance, increased fall risk, and a markedly diminished quality of life.
Previous attempts to address this using powered ankle exoskeletons or exosuits have, despite considerable research investment, consistently failed to reduce the metabolic cost of walking in portable form. The ankle’s distance from the body’s centre of mass makes it biomechanically and energetically costly to assist – mass at the ankle carries four times the metabolic penalty of equivalent mass at the trunk.
A different approach: Target the hip
The University of Utah team, led by senior author Tommaso Lenzi, associate professor of Mechanical Engineering, chose a different anatomical target. Their portable bilateral hip exoskeleton, weighing 2.63kg in total, straps around the pelvis and thighs and uses battery-powered motors to assist both flexion and extension at each hip joint, independently tuned for each participant.
The rationale is mechanistically sound. Individuals with hemiparesis typically compensate for impaired ankle push-off by recruiting their hip joints to generate additional propulsive energy – a strategy that is metabolically costly. By offloading the hips, the device targets the compensatory mechanism directly.
“Portable ankle exoskeletons have failed to reduce the energy required for stroke patients to walk, so we proposed a different approach,” said lead author Kai Pruyn, a graduate student in Lenzi’s HGN Lab for Bionic Engineering. “Patients with ankle weakness often compensate with their hip joints, which requires extra energy. Our goal was to develop a powerful and fully portable hip exoskeleton. We found that the hip assistance effectively compensated for reduced ankle propulsion.”
Like removing a 13.5kg backpack
Seven participants with chronic post-stroke hemiparesis completed treadmill walking trials with and without the powered exoskeleton. The average net metabolic rate fell an average of 18% when comparing walking without the device to walking with it. The reduction was consistent across all participants. The authors noted that this result is “equivalent to removing a 13.5kg backpack from a healthy individual. For someone with hemiparesis, that’s a life-changing difference.”
As the authors note, this “provides important mechanistic insight into how hip assistance influences walking energetics post-stroke, demonstrating effective offloading of the user’s joints.”
“Improving quality of life after a stroke is one of the biggest unmet challenges in healthcare today,” said Lenzi. “We’re now showing that robotics can make a measurable impact here.”
The team is now working with partners in prosthetics and orthotics to develop a version suitable for home and community use, with the aim of supporting activities beyond level treadmill walking.
The authors noted that future work should explore human-in-the-loop optimisation and AI-based adaptive controllers.
Reference:
Pruyn, K., Murray, R., Gabert, L., et al. (2026). Portable hip exoskeleton improves walking economy for stroke survivors. Nature Communications.
https://doi.org/10.1038/s41467-026-69580-0
